U.S. patent application number 13/705063 was filed with the patent office on 2013-06-27 for access point power control.
This patent application is currently assigned to Ubiquisys Limited. The applicant listed for this patent is Ubiquisys Limited. Invention is credited to Alan Carter, Aminu Wada Maida, Stephen Whittaker.
Application Number | 20130165175 13/705063 |
Document ID | / |
Family ID | 37891251 |
Filed Date | 2013-06-27 |
United States Patent
Application |
20130165175 |
Kind Code |
A1 |
Carter; Alan ; et
al. |
June 27, 2013 |
ACCESS POINT POWER CONTROL
Abstract
There is described a method of controlling a basestation in a
cellular wireless communications network, the method comprising,
within the basestation, autonomously and dynamically adapting a
maximum value for a total transmit power of the basestation, such
that interference between the basestation and other access points
in the vicinity is minimized.
Inventors: |
Carter; Alan; (Swindon,
GB) ; Whittaker; Stephen; (Newbury, GB) ;
Maida; Aminu Wada; (Swindon, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ubiquisys Limited; |
Swindon |
|
GB |
|
|
Assignee: |
Ubiquisys Limited
Swindon
GB
|
Family ID: |
37891251 |
Appl. No.: |
13/705063 |
Filed: |
December 4, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13214084 |
Aug 19, 2011 |
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13705063 |
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11801337 |
May 8, 2007 |
8032142 |
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13214084 |
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Current U.S.
Class: |
455/522 |
Current CPC
Class: |
H04W 52/146 20130101;
H04W 52/367 20130101; H04W 24/02 20130101; H04W 52/225 20130101;
H04W 52/24 20130101; H04W 88/08 20130101; H04W 84/045 20130101;
H04W 52/143 20130101; H04W 52/343 20130101; H04W 52/346
20130101 |
Class at
Publication: |
455/522 |
International
Class: |
H04W 52/04 20060101
H04W052/04; H04W 88/08 20060101 H04W088/08 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 2, 2007 |
GB |
0702094.4 |
Claims
1. A method of controlling a basestation in a cellular wireless
communications network comprising macrocells and femtocells, the
method comprising: obtaining measurements made by user equipment
devices of signals from other basestations of said network;
determining from said measurements made by user equipment devices
whether there has been a significant change in interference in a
femtocell layer or a macrocell layer; if there has been a
significant change in interference, rerunning algorithms performed
on power up for selection of a carrier, a scrambling code, and/or
maximum total uplink and downlink powers; and if there has not been
a significant change in interference, adapting a maximum value for
a total transmit power of the basestation based on said
measurements made by user equipment devices.
2. A method as claimed in claim 1, further comprising adapting said
maximum value for the total transmit power autonomously and
dynamically within the basestation.
3. A method as claimed in claim 1, further comprising adapting said
maximum value for the total transmit power based on: knowledge of
the transmit power of, and path loss to, surrounding macrolayer
basestations and other basestations, said knowledge being derived
from information decoded from broadcast channel transmissions
thereof and measured received signal strengths.
4. A method as claimed in claim 1, further comprising adapting said
maximum value for the total transmit power based on: knowledge of
whether a measured dominant interferer is a macrolayer basestation
or a nearby access point.
5. A method as claimed in claim 4, wherein said knowledge of
whether a measured dominant interferer is a macrolayer basestation
or a nearby access point is based on identity information conveyed
in the received broadcast channel of said interferer and RF signal
measurements therefrom.
6. A method as claimed in claim 1, further comprising adapting said
maximum value for the total transmit power based on: knowledge of
historical statistics for the path loss between said basestation
and permitted User Equipments (UEs) in call therewith said
basestation, and based on a predetermined maximum permitted path
loss figure.
7. A method as claimed in claim 1, further comprising adapting said
maximum value for the total transmit power based on: knowledge of
historical statistics for a received signal/interference ratio as
measured at UEs in call with the basestation, and based on a
predetermined minimum signal/interference ratio.
8. A method as claimed in claim 7, wherein measurements of said
received signal/interference ratio are specifically requested by
the basestation.
9. A method as claimed in claim 1, further comprising adapting said
maximum value for the total transmit power based on: knowledge of
historical statistics for a path loss between UEs in call with the
basestation and nearby nodeBs.
10. A method as claimed in claim 9, wherein measurements of said
path loss are specifically requested by the basestation.
11. A method as claimed in claim 1, further comprising adapting
said maximum value for the total transmit power based on: knowledge
of round trip delays for a communications path between said
basestation and a user terminal within a target coverage area, and
based on a predetermined maximum permitted round-trip delay.
12. A method as claimed in claim 1, further comprising adapting
said maximum value for the total transmit power based on: knowledge
of access attempts by non-permitted users.
13. A method as claimed in claim 1, wherein, before the step of
adapting a maximum value for a total transmit power of the
basestation, there is the step of: determining whether or not a
carrier that has been selected for communicating with UEs is unused
by neighbouring macrolayer basestations or other basestations;
wherein a carrier is unused if there are no detected macrolayer
basestation or other basestation CPICH signals and the received
signal strength indicator (RSSI) on the carrier is below a minimum
interference threshold.
14. A method as claimed in claim 13, further comprising the step
of: if the carrier is not unused by neighbouring macrolayer
basestations or other basestations, determining whether the
interference caused by neighbouring macrolayer basestations is
greater than or less than the interference caused by neighbouring
other basestations.
15. A method as claimed in claim 14, said adapting step comprising:
if said carrier is unused by neighbouring macrolayer basestations
or other basestations, setting the total transmit power of the
basestation at a first level; if said carrier is not unused by
neighbouring macrolayer basestations or other basestations, and the
interference caused by neighbouring macrolayer basestations is
greater than the interference caused by neighbouring other
basestations, setting the total transmit power of the basestation
at a second level; and if said carrier is not unused by
neighbouring macrolayer basestations or other basestations, and the
interference caused by neighbouring macrolayer basestations is less
than the interference caused by neighbouring other basestations,
setting the total transmit power of the basestation at a third
level.
16. A method as claimed in claim 15, further comprising:
determining whether said first, second or third levels are greater
than a maximum permitted power threshold; and if said first, second
or third levels are greater than a maximum permitted power
threshold, resetting the total transmit power of the basestation to
said maximum permitted power threshold; and if said first, second
or third levels are not greater than a maximum permitted power
threshold, maintaining the total transmit power of the basestation
at its set level.
17. A basestation adapted to perform the method according to any of
claims 1-16.
Description
[0001] This divisional application claims priority to U.S. patent
application Ser. No. 13/214,084, filed on Aug. 19, 2011, and
entitled ACCESS POINT POWER CONTROL, which is a continuation of
U.S. patent application Ser. No. 11/801,337, filed on May 8, 2007,
now U.S. Pat. No. 8,032,142, issued on Oct. 4, 2011, and entitled
"ACCESS POINT POWER CONTROL", which is hereby incorporated by
reference and for all purposes.
[0002] This invention relates to an access point, acting as a
basestation in a cellular wireless communications network, and in
particular to such an access point, in which maximum transmit power
levels of the access point are controlled in such a way as to avoid
interference while ensuring acceptable coverage.
[0003] In conventional cellular networks, basestations are
installed by the network operators, in order to provide coverage
for the areas where the network operators expect there to be a
demand for their services. The network planners are able to choose
the locations of the basestations, and are able to set the maximum
transmit powers, of the basestation itself and of the mobile
devices that establish connections with the basestation, in order
to ensure a certain coverage and Quality of Service (QoS). To
achieve these aims, the process requires detailed site surveys and
geographical planning. When a maximum transmit power has been set,
this effectively sets the size of the cell served by the
basestation, because it determines the range over which the
transmissions from the basestation can successfully be received.
The maximum transmit power is rarely changed after it has initially
been set, but can be altered from the network if necessary, for
example because of changes to the radio network.
[0004] When a maximum transmit power has been set for the
basestation, and calls are in progress, power control is also
applied to the transmissions within these calls. Firstly, an
initial transmit power is set, for example based on the power of a
received access request, and thereafter power control is applied to
the transmissions, based on signal strength measurements made by
the mobile device involved in the call and reported back to the
basestation. Such power control can operate very quickly. For
example, the power level used by a basestation for its
transmissions can be adapted at a frequency in the kilohertz
region. That is, the power level can in theory change many times
per second if the signal strength measurements indicate this.
[0005] In the case of access points (also known as femtocell
basestations), these are intended to be available for purchase by
consumers themselves for location within a home or office, and are
intended to provide cellular coverage over relatively small
geographical areas, for example only within the building in which
they are located. For such devices, costly site surveys and
detailed radio network planning are not possible. It is therefore
proposed that such devices should be able to configure themselves,
based on the local radio environment.
[0006] U.S. Pat. No. 6,314,294 relates to a basestation, in which
RF transmit power levels are self calibrated, using data collected
by the wireless system.
[0007] According to a first aspect of the present invention, there
is provided method of controlling a basestation in a cellular
wireless communications network, the method comprising: [0008]
within the basestation, autonomously and dynamically adapting a
maximum value for a total transmit power of the basestation.
[0009] According to a second aspect of the present invention, there
is provided a basestation adapted to perform the method according
to the first aspect of the invention.
[0010] This has the effect that the basestation can configure
itself, based on the local radio environment, with reduced network
involvement.
[0011] For a better understanding of the present invention, and to
show how it may be put into effect, reference will now be made, by
way of example, to the accompanying drawings, in which:
[0012] FIG. 1 is a block schematic diagram of a part of a cellular
wireless communications network.
[0013] FIG. 2 is a flowchart of a carrier-selection algorithm.
[0014] FIG. 3 is a flowchart of a scrambling code selection
algorithm.
[0015] FIG. 4 is a flowchart of an algorithm for selecting the
initial downlink maximum transmit power.
[0016] FIG. 5 is a flowchart of an algorithm for selecting the
initial uplink maximum transmit power.
[0017] FIG. 6 is a flowchart of an algorithm for adapting the
uplink and downlink maximum transmit powers.
[0018] FIG. 7 is a flowchart of an algorithm for adapting the
uplink and downlink maximum transmit powers in the event that
macrolayer interference is detected.
[0019] FIG. 8 is a flowchart of an algorithm for adapting the
uplink and downlink maximum transmit powers in the event that no
interference is detected in the macrolayer or the femtocell
basestation layer.
[0020] FIG. 1 illustrates a part of a cellular wireless
communications network in accordance with an aspect of the present
invention. Specifically, FIG. 1 shows a core network (CN) 10 and a
radio network (RN) 12 of a cellular wireless communications
network. These are generally conventional, and are illustrated and
described herein only to the limited extent necessary for an
understanding of the present invention.
[0021] Thus, the core network 10 has connections into the Public
Switched Telephone Network (PSTN) (not shown) and into a packet
data network, for example the internet 14. The radio network 12 may
include, for example, a GSM radio network and/or a UMTS radio
network, which are then generally conventional. As shown in FIG. 1,
the radio network 12 has a basestation (BS) 16 connected thereto.
As will be recognized by the person skilled in the art, a typical
radio network 12 will have many such basestations connected
thereto. These basestations provide coverage over respective
geographic areas, or cells, such that a service is available to
subscribers. Often, there is a group of basestations that together
provide coverage to the whole of the intended service area, while
other basestations provide additional coverage to smaller areas
within that intended service area, in particular to smaller areas
where there is expected to be more demand for the service. The
cells served by the basestations of the first group are then
referred to as macrocells, while the smaller areas served by the
additional basestations are referred to as microcells.
[0022] FIG. 1 also shows an additional basestation 18 that can be
used to provide coverage over a very small area, for example within
a single home or office building. This is referred to as a
femtocell basestation (FBS). The femtocell basestation 18 is
connected into the mobile network operator's core network 10 over
the internet 14, by means of the customer's existing broadband
internet connection 20. Thus, a user of a conventional mobile phone
22 can establish a connection through the femtocell basestation 18
with another device, in the same way that any other mobile phone
can establish a connection through one of the other basestations of
the mobile network operator's network, such as the basestation
16.
[0023] The core network 10 includes a management system (MS) 24
that provides information to the FBS 18, as described in more
detail below.
[0024] As mentioned above, the macrocell basestations provide
coverage to the whole of the intended service area including the
location of the femtocell basestation 18 and the location of the
mobile phone 22 while it is in the coverage area of the femtocell
basestation 18. However, the network is configured such that, when
a mobile device that is registered with the femtocell basestation
18 is within the coverage area of the femtocell basestation 18,
then it will preferentially establish a connection with the
femtocell basestation 18 rather than with the macrolayer
basestation 16.
[0025] When the femtocell basestation 18 is first powered on, it
selects a carrier frequency and a scrambling code, from lists
provided to it from a management system that generally controls the
operation of the femtocell basestations in the network. The carrier
frequencies and the scrambling codes on the list are shared with
other basestations in the network, including nodeBs of the
macrolayer and other femtocell basestations, and so the carrier
frequency and scrambling code are chosen such that they result in
the lowest interference to neighbour nodeBs of the macrolayer and
neighbour femtocell basestations.
[0026] Thereafter, the basestation can autonomously and dynamically
select its carrier frequency from the permitted set of carrier
frequencies, and can autonomously and dynamically select its
scrambling code from a permitted set of codes, in order to produce
the lowest interference (see FIGS. 2 and 3).
[0027] Also, the femtocell basestation 18 selects an initial value
for the maximum total downlink power, and for total mobile transmit
power levels (see FIGS. 4 and 5). This initial value can be preset
in the femtocell basestation 18, based for example on an assumption
about the type of location in which the device will be used. For
example, it may be assumed that the device will generally be used
in homes or small offices, up to a particular size (for example 90
to 250 m.sup.2), and further assumptions can then be made about the
signal attenuation that will result, and this can be used to
determine what value should be set for the maximum total downlink
power, in order to ensure a reasonable coverage throughout that
area, while avoiding interference with neighbour nodeBs of the
macrolayer and neighbour femtocell basestations.
[0028] Again, the femtocell basestation 18 can autonomously and
dynamically adapt both its total transmit power (including the
transmit power of control channels as well as traffic channels) and
the total transmit power of the mobiles attached to the
basestation.
[0029] It is well known that power control should be applied in a
cellular communications system, so that the transmission powers in
the uplink (UL) and downlink (DL) directions can be adjusted
quickly, in order to take account of rapid changes that affect each
communication path from the basestation to the relevant mobile
device. In the UMTS system, the group of functions used to achieve
this are: open-loop power control, inner-loop (or fast) PC and
outer-loop power control in both UL and DL directions. Slow power
control is also applied to the DL common channels. Open-loop power
control is responsible for setting the initial UL and DL
transmission powers when a UE is accessing the network. There are
two types of inner-loop power control algorithms both of which
adjust the transmission dynamically on a 1500 Hz basis. The
outer-loop power control estimates the received quality and adjusts
the target SIR (signal-interference ratio) for the fast closed-loop
power control so that the required quality is provided.
[0030] However, in accordance with aspects of the present
invention, the total transmit power of the basestation (including
the transmit power of control channels as well as traffic channels)
and the total transmit power of the mobiles attached to the
basestation are also adaptively controlled autonomously by the
basestation itself.
[0031] This control can for example take place on the basis of
measurements made by the basestation itself. That is, the
basestation is able to detect signals transmitted by other
basestations, including macrolayer basestations and other femtocell
basestations. The basestation can identify whether a detected
interferer is a macrolayer basestation or a femtocell basestation
based on identity information conveyed in the received broadcast
channel of said interferer and RF signal measurements therefrom.
Preferably, the basestation suspends its own transmissions
temporarily in order to make these measurements, both when it is
initially powered on, and then intermittently during operation.
[0032] Thus, at power up the RSCP (Received Signal Code Power)
values can be determined for the CPICHs (Common Pilot Channels) of
all surrounding femtocell basestations and macrolayer nodeBs for
all available carriers. The carrier exhibiting the lowest
interference is selected, where the lowest interference is defined
as follows.
[0033] FIG. 2 is a flowchart showing the preferred algorithm by
which the femtocell basestation may select the initial carrier.
[0034] In the first step 50, the interference is calculated for
each of the allowed carriers on the macrolayer (ML) and each of the
allowed carriers on the femtocell basestation layer (FBL). The
macrolayer interference for each carrier is calculated by
determining the macrolayer CPICH_RSCPs in milliwatts for each
detected scrambling code in each carrier. These individual
macrolayer CPICH_RSCPS are added together to calculate the total
macrolayer interference power per carrier. This value is then
converted back to dBm.
[0035] A similar method is used for determining the femtocell
basestation layer interference for each carrier. The femtocell
basestation layer CPICH_RSCPs are determined in milliwatts for each
detected scrambling code in each carrier. These individual
femtocell basestation CPICH_RSCPs are added together to calculate
the total femtocell basestation interference power per carrier.
This value is then converted back to dBm.
[0036] In the next step 52, it is determined whether there is more
than one allowed carrier.
[0037] If there is only one allowed carrier, the process moves to
step 54, that of determining whether the macrolayer interference
for that carrier is below a maximum macrolayer interference
threshold. If it is, the carrier is selected by the femtocell
basestation. If the interference is above the threshold, an error
is generated.
[0038] If there is more than one allowed carrier, the process moves
to step 56, that of determining whether any of the allowed carriers
on the macrolayer are currently unused. Hereinafter, a carrier is
considered unused on the macrolayer if there are no detected nodeB
CPICH signals and received signal strength indicator (RSSI) on the
carrier is below a minimum macrolayer interference threshold.
[0039] If there are allowed carriers unused on the macrolayer, the
process then determines in step 58 whether or not there are any
allowed carriers on the femtocell basestation layer. Hereinafter, a
carrier is considered unused on the femtocell basestation layer if
there are no detected femtocell basestation CPICH signals and the
RSSI on the carrier is below a minimum femtocell basestation layer
interference threshold. If there are unused allowed carriers on the
femtocell basestation layer, the femtocell basestation layer
carrier with the lowest RSSI is chosen. If there are no unused
allowed carriers on the femtocell basestation layer, the femtocell
basestation layer carrier with the lowest interference (as
calculated in step 50) is chosen.
[0040] In step 56, if it is determined that there are no unused
carriers on the macrolayer, the process moves to step 60, where the
carrier with the least macrolayer interference (as calculated in
step 50) is chosen. In step 62, the macrolayer interference of this
carrier is compared with a maximum macrolayer interference
threshold. If the interference is below the threshold, that carrier
is chosen. If the interference is above the threshold, an error is
generated.
[0041] Once the carrier has been selected then, from the list of
available scrambling codes, a code is selected. For example, the
CPICH_RSCPs of all the available codes may be ranked, and the code
with the lowest CPICH_RSCP value selected.
[0042] FIG. 3 is a flowchart showing the preferred algorithm by
which the scrambling code may be selected. This algorithm will
typically be applied after the carrier selection algorithm
described above with reference to FIG. 2.
[0043] In step 70, the interference for each allowed scrambling
code for the selected carrier is calculated. This step is performed
by grouping and summing, by scrambling code, the detected femtocell
basestation CPICH RSCPs for each basestation using the selected
carrier.
[0044] In step 72, the process determines whether or not there are
any scrambling codes that are not being used by the detected
femtocell basestations. If there are any unused codes, one of these
is chosen as the scrambling code. The selection of scrambling code
from the list of unused codes is randomized to minimize the
probability of two collocated access points selecting the same
code.
[0045] If there are no unused codes the process moves to step 74,
where the code with the least interference (as calculated in step
70) is selected. If the interference on this code is less than a
maximum threshold, that code is chosen. If the interference is
above the maximum threshold, an error is generated.
[0046] Further, the initial selection of carrier and scrambling
code could be changed based on measurements from the UE. The UE may
report measurements from an adjacent carrier that may indicate that
the initial carrier or scrambling code were not optimal due to
local shadowing of the femtocell basestation.
[0047] Following the carrier and code selection algorithms, the
radio measurement data is reported back to the central management
system, where it is checked against specified thresholds. If it is
determined that the interference levels for the selected
code/carriers exceed a predefined threshold set by the management
system, and hence that the basestation is not in a location where
it can perform acceptably, an error message is supplied to the
user, suggesting a repositioning of the unit to a more optimal
position within the home.
[0048] The initial maximum power values can then be set. If the
macrolayer interference dominates, then the initial maximum Down
Link transmit power is set based on the strongest macrolayer CPICH
RSCP level and including a nominal in-door path loss of typically
60 dB. Alternatively, if a carrier is selected which has little or
no macrolayer interference, the maximum DL transmit power is set at
the same level as the neighbour femtocell basestation exhibiting
the strongest CPICH RSCP level (i.e. the largest femtocell
basestation interferer). This is done to maintain the same QoS for
collocated femtocell basestations. If there is neither macrolayer
or femtocell basestation interference, then the initial maximum DL
transmit power is set according to the expected UE sensitivity (for
a mid range data service) including a nominal indoor path loss of
60 dB. This is different to existing Radio Access Network (RAN)
design practice, in which the maximum DL Transmit power is set by a
RF planner to ensure the expected coverage.
[0049] The maximum Up Link femtocell basestation UE transmit power
is firstly calculated by determining the smallest path loss to the
neighbouring macrolayer nodeB, typically the closest. By summing
the minimum macrolayer nodeB sensitivity with the smallest path
loss, the maximum UL Tx power can be calculated. This method keeps
the noise rise caused by the femtocell basestation UE below the
noise caused by the macrolayer cell traffic. Likewise if no
macrolayer interference is detected then the femtocell basestation
sets its maximum DL transmit power at the same level as the
neighbour femtocell basestation exhibiting the strongest CPICH RSCP
level. If there is neither macrolayer or femtocell basestation
interference then the initial UL transmit power is set according to
the femtocell basestation sensitivity (for a mid range data
service) and a nominal path loss of 60 dB. Again, this is quite
different to existing Radio Access Network (RAN) design, in which
the maximum UL Transmit power is set by a RF planner to ensure the
expected coverage and UE battery life.
[0050] FIG. 4 is a flowchart showing the preferred algorithm by
which the femtocell basestation may select the initial DL maximum
transmit power.
[0051] In step 100, the interference is calculated for the selected
carrier on the femtocell basestation layer and the macrolayer. This
step will already have been performed during the carrier-selection
algorithm (step 50 in FIG. 2).
[0052] In step 102, it is determined whether the selected carrier
is unused on the macrolayer and the femtocell basestation layer.
Again, this step will already have been performed during the
carrier-selection algorithm (steps 56 and 58 in FIG. 2).
[0053] If the carrier is unused on the macrolayer and the femtocell
basestation layer, the initial DL maximum transmit power is set at
UE.sub.Prx, min, the average minimum signal power required by a
femtocell basestation UE to support a particular data or speech
service, plus the minimum indoor loss, a parameter corresponding to
the allowed indoor path loss that will provide the required
coverage (step 104). The minimum indoor loss is supplied by a
central management system.
[0054] If the selected carrier is not unused by the macrolayer or
the femtocell basestation layer, the process moves to step 106
where the macrolayer interference is compared with the femtocell
basestation interference for the selected carrier. If the
macrolayer interference is greater, in step 108 the initial DL
maximum transmit power is set at the minimum indoor loss (as
described above), plus the RSCP value of the nodeB with the largest
detected RSCP, minus 10.times.log.sub.10(percentage of the total
femtocell basestation power allocated to CPICH).
[0055] The percentage of the total downlink transmission power
allocated to the CPICH is a parameter supplied by the central
management system.
[0056] If, in step 106, it is determined that the femtocell
basestation interference is greater than the macrolayer
interference, the initial DL maximum transmit power is set in step
110 at the CPICH power of the neighbour femtocell basestation with
the largest detected RSCP value, minus
10.times.log.sub.10(percentage of the total femtocell basestation
power allocated to CPICH).
[0057] As before, the percentage of the total downlink transmission
power allocated to the CPICH is a parameter supplied by the
management system.
[0058] Once the initial DL maximum transmit power has been set in
one of steps 104, 108 or 110, the process checks in step 112
whether the initial DL maximum transmit power is greater than or
less than the maximum permitted femtocell basestation DL power (a
parameter set by the management system). If it is less than the
maximum permitted power, the initial DL maximum transmit power
remains at its original value. However, if the initial DL maximum
transmit power is greater than the maximum permitted power, the
initial DL maximum transmit power is reset at the maximum permitted
power, and a warning sent to the management system. For example, a
flag may be set to indicate that the initial DL maximum transmit
power is less than that required to run a particular speech or data
service, or that the DL power is currently at its maximum permitted
level.
[0059] FIG. 5 is a flowchart showing the preferred algorithm by
which the femtocell basestation may select the initial UL maximum
transmit power.
[0060] Steps 150 and 152 are calculating the interference for the
selected carrier on the femtocell basestation later and the
macrolayer, and checking whether the selected carrier is in use on
the femtocell basestation layer or the macrolayer, respectively.
Both of these steps will have been carried out earlier as part of
the carrier selection algorithm, and are described in more detail
with reference to FIG. 2.
[0061] If the carrier is not in use on the macrolayer or the
femtocell basestation layer, the initial UL maximum transmit power
is set in step 154 at FB.sub.Prx, min, the average minimum signal
power required by a femtocell basestation to support a particular
data or speech service, plus the minimum indoor loss, the allowed
indoor path loss that will provide the required coverage.
[0062] If the carrier is in use on the femtocell basestation layer
or the macrolayer, the process moves to step 156, where the
macrolayer interference is compared with the femtocell basestation
layer interference for the selected carrier. If the femtocell
basestation interference is greater, the initial UL maximum
transmit power is set in step 158 at the maximum UE transmit power
of the femtocell basestation with the least path loss. This value
is determined by first calculating the path losses from the
femtocell basestation to the detected femtocell basestations using
the following equation:
L.sub.FB-FB=CPICH.sub.--Tx_Power.sub.FB-CPICH.sub.--RSCP.sub.FB
where CPICH_Tx_Power.sub.FB is the CPICH transmitted power read
from the broadcast channel of detected femtocell basestations. The
maximum UE transmit power read from the broadcast channel of the
neighbour femtocell basestation that has the least path loss to the
femtocell basestation is then selected.
[0063] If the macrolayer interference is greater than the femtocell
basestation interference for the selected carrier, the nodeB to
femtocell basestation path losses are then calculated in step 160.
The path losses are calculated using the following equation:
L.sub.NodeB-FB=CPICH.sub.--Tx_Power.sub.NodeB-CPICH.sub.--RSCP.sub.NodeB
where CPICH_Tx_Power.sub.NodeB is the CPICH transmitted power read
from the broadcast channel of detected nodeBs.
[0064] The initial UL maximum transmit power is set in step 164 at
ML.sub.Prx, min, the average minimum signal power required by a
nodeB to support a particular data or speech service, plus the RSCP
value that corresponds to the least nodeB to femtocell basestation
path loss.
[0065] Once the initial UL maximum transmit power has been set in
one of steps 154, 158 or 164, the process moves to step 166, where
the initial UL maximum transmit power is compared with the maximum
permitted femtocell basestation UL power. If the UL maximum
transmit power is less than the maximum permitted power, the
initial UL maximum transmit power is maintained at its original
level. If the UL maximum transmit power is greater than the maximum
permitted power, the initial UL maximum transmit power is reset at
the maximum permitted power as defined by the management system.
Also, a warning is sent to the management system, that the UL power
may be insufficient for certain data or speech services, or that
the UL power is currently at its maximum permitted level.
[0066] During operation, the maximum DL and UL transmit powers are
adapted through the regular CPICH RSCP and CPICH Ec/Io measurements
reported by the femtocell basestation UEs during idle mode or RRC
connected mode (CELL_DCH state). The adaptation algorithm assumes
that the femtocell basestation UEs remain for the majority of the
time within the expected coverage area (i.e. the house or office).
The adaptation algorithm slowly increases or decreases the allowed
UL and DL maximum transmit power level to ensure that the CPICH
Ec/Io (or QoS) remains at a suitable level for both speech and data
services. In the case that the femtocell basestation detects that
there is local macrolayer interference then over a period of time
it builds two sets of histograms from the femtocell basestation UE
measurements of the active and neighbour cells. The first histogram
is the path loss between the femtocell basestation UE and the
neighbour macrolayer nodeB and the second set of histograms is the
path loss between the femtocell basestation UE and the femtocell
basestation and also the femtocell basestation UE CPICH Ec/Io
measurements. The adaptation algorithm attempts to keep typically
90% of all femtocell basestation UE CPICH Ec/Io measurements above
a particular level (e.g. -10 to -15 dB) but will only allow 1% of
femtocell basestation UE to femtocell basestation path loss
measurements (i.e. largest path loss) to exceed the path loss
between the femtocell basestation UE and macrolayer nodeB (i.e.
smallest path loss). Furthermore the adaptation algorithm will
allow a maximum path femtocell basestation to femtocell basestation
UE path loss of typically <90 dB for 95% of the time. By
assuming that the UL and DL path loss is reciprocal, the same
adaptation algorithms are used to set the maximum DL and UL
transmit power levels.
[0067] The femtocell basestation may also gather UE measurements by
`sniffing` periodically (for example every 100 seconds) by stealing
a down link frame.
[0068] FIG. 6 is a flowchart showing the preferred algorithm by
which the femtocell basestation may dynamically adapt the UL and DL
maximum transmit powers.
[0069] As described above, the femtocell basestation regularly
takes UE measurements of the active and neighbour cells, and these
are used as the input for adapting the maximum transmit powers. By
monitoring the UE measurements, in step 200, the process first
determines whether there has been a significant change on either
the macrolayer or the femtocell basestation layer's interference
levels for the carrier and scrambling code already selected. A
significant change in this context means any change that will
require a new carrier and/or scrambling code to be reselected.
Therefore, if a significant change is found, the process will rerun
the carrier-selection algorithm, the scrambling-code-selection
algorithm and the initial power setup algorithm described with
reference to FIGS. 2, 3 and 4, respectively, in step 202.
[0070] Once these "power up" algorithms have been performed, the
process moves to step 203, that of re-gathering samples of UE
measurements so that step 200 can be performed again for the new
carrier and/or scrambling code.
[0071] If there is no significant change in the macrolayer or the
femtocell basestation layer, the process determines in step 204
whether or not the carrier is used on the macrolayer. If the
carrier is used on the macrolayer (i.e. interference is detected on
the macrolayer), the macrolayer interference algorithm is used to
adapt the power (see FIG. 7).
[0072] If the carrier is not used on the macrolayer, the process
determines in step 206 whether the carrier is used on the femtocell
basestation layer. If the carrier is not used on the femtocell
basestation layer (i.e. there is no interference on the femtocell
basestation layer) the "no interference" algorithm is used to adapt
the power (see FIG. 8).
[0073] If the carrier is used on the femtocell basestation layer,
the UL and DL maximum transmit powers are set as follows.
[0074] The UL maximum transmit power is set at the maximum UE
transmit power of the femtocell basestation with the least path
loss. This value is determined by first calculating the path losses
from the femtocell basestation to the surrounding detected
femtocell basestations. The maximum UE transmit power read from the
broadcast channel of the surrounding femtocell basestation that has
the least path loss to the femtocell basestation is then
selected.
[0075] The path losses are determined, as before, by the following
equation:
L.sub.FB-FB=CPICH.sub.--Tx_Power.sub.FB-CPICH.sub.--RSCP.sub.FB.
[0076] The DL maximum transmit power is set at the CPICH Tx power
of the femtocell basestation with the largest detected RSCP value,
minus 10.times.log.sub.10(percentage of the total femtocell
basestation power allocated to CPICH).
[0077] That is, if only interference from a neighbouring femtocell
basestation is detected, the basestation uses the power of that
neighbouring basestation to set its own UL and DL maximum transmit
powers.
[0078] FIG. 7 is a flowchart of the preferred algorithm that may be
used to adapt the UL and DL maximum transmit powers in the event
that macrolayer interference is detected.
[0079] As described above, histograms are produced from the UE
measurements. Specifically, these are the femtocell basestation UE
to neighbouring nodeB path losses, the femtocell basestation to
femtocell basestation UE path losses, and the femtocell basestation
UE CPICH Ec/Io measurements. From these histograms, the following
quantities can be calculated:
[0080] Avg_Ec/Io=the average of the top 10% femtocell basestation
UE CPICH Ec/Io values;
Avg_ML_Pathloss=the average of the bottom 1% nodeB to femtocell
basestation UE path losses; Avg_FBL_Pathloss=the average of the top
10% FB to FB UE path losses; Pathloss_adjustment=the absolute value
of [1/2.times.(Avg_FBL_Pathloss-Avg_ML_Pathloss)]
[0081] Further, a new parameter, Indoor loss, is set to the value
of minimum indoor loss, initially provided by the central
management system. However, minimum indoor loss is adapted as the
process of DL and UL maximum power adaptation is repeated, as will
be described in more detail below.
[0082] In step 250, Avg_Ec/Io is compared with the desired
femtocell basestation UE CPICH Ec/Io. If Avg_Ec/Io is larger, then
the process moves to step 252, which compares Avg_ML_Pathloss with
Avg_FBL_Pathloss. If Avg_ML_Pathloss is greater, the UL and DL
maximum transmit powers are kept at the same level (step 254).
[0083] If Avg_ML_Pathloss is smaller than Avg_FBL_Pathloss, then
the UL and DL maximum transmit powers are set as follows (step
256). Maximum DL power is set at the RSCP level of the largest
detected nodeB RSCP value, minus 10.times.log.sub.10(percentage of
the total femtocell basestation power allocated to CPICH), plus the
indoor loss, minus Pathloss_adjustment. Maximum UL power is set at
ML.sub.Prx, min, the minimum signal power required by the
basestation to support a particular data or speech service, plus
the Avg_ML_Pathloss. Further, minimum indoor loss is re-set at the
value of Indoor loss minus Pathloss_Adjustment.
[0084] If it is determined, in step 250, that Avg_Ec/Io is less
than the desired femtocell basestation UE CPICH Ec/Io, the process
moves to step 258, where Avg_ML_Pathloss is again compared with
Avg_FBL_Pathloss.
[0085] If Avg_ML_Pathloss is smaller, the maximum DL power is set
in step 260 at the RSCP value of the nodeB with the largest
detected RSCP value, minus 10.times.log.sub.10(percentage of the
total femtocell basestation power allocated to CPICH), plus the
Avg_ML_Pathloss. The maximum UL power is set at ML.sub.Prx, min,
the minimum signal power required by the basestation to support a
particular data or speech service, plus the Avg_ML_Pathloss.
[0086] If Avg_ML_Pathloss is greater than Avg_FBL_Pathloss, the
maximum DL power is set in step 262 at the RSCP value of the nodeB
with the largest RSCP value, minus 10.times.log.sub.10(percentage
of the total femtocell basestation power allocated to CPICH), plus
the indoor loss and Pathloss_adjustment. The maximum UL power is
set at ML.sub.Prx, min, the minimum signal power required by a
femtocell basestation to support a particular data or speech
service, plus the Avg_ML_Pathloss. Further, minimum indoor loss is
re-set at the value of Indoor loss plus Path loss_Adjustment.
[0087] Once the maximum DL and UL powers have been set in one of
steps 256, 260 or 262, the process moves in parallel to steps 263
and 264. In step 263 the process checks whether the maximum DL
power is greater than or less than the maximum permitted femtocell
basestation DL power (a parameter set by the management system). If
it is less than the maximum permitted power, the maximum DL power
remains at its re-set value. However, if the maximum DL power is
greater than the maximum permitted power, the maximum DL power is
changed to the maximum permitted power, and a warning sent to the
management system. For example, a flag may be set to indicate that
the maximum DL power is less than that required to run a particular
speech or data service.
[0088] In step 264 the process checks whether the maximum UL power
is greater than or less than the maximum permitted femtocell
basestation UL power (a parameter set by the management system). If
it is less than the maximum permitted power, the maximum UL power
remains at its re-set value. However, if the maximum UL power is
greater than the maximum permitted power, the maximum UL power is
changed to the maximum permitted power, and a warning sent to the
management system. For example, a flag may be set to indicate that
the maximum UL power is less than that required to run a particular
speech or data service.
[0089] The whole process as described by FIGS. 6 and 7 repeats,
adapting the maximum UL and DL powers until either an error event
occurs, the powers converge to an optimal value, or the host
processor identifies that there has been a significant change in
the local interference levels and the carrier, scrambling code and
initial UL and DL powers need to be re-evaluated.
[0090] Further, the value of minimum indoor loss is adapted as the
process repeats. For example, minimum indoor loss may be set at 60
dB initially. When the process is run, it may end up at step 262.
If Pathloss_Adjustment is found to be 10 dB, minimum indoor loss is
reset at 70 dB, and for the next repeat of the process, indoor loss
will begin at 70 dB.
[0091] FIG. 8 is a flowchart of the preferred algorithm that may be
used to adapt the UL and DL maximum transmit powers in the event
that no interference is detected from the macrolayer or the
femtocell basestation layer.
[0092] As described above, histograms are produced from the UE
measurements. Specifically, these are the femtocell basestation to
femtocell basestation UE path losses, and the femtocell basestation
UE CPICH Ec/Io measurements. From these histograms, the following
quantities can be calculated:
[0093] Avg_Ec/Io=the average of the top 10% femtocell basestation
UE CPICH Ec/Io values; Avg_FBL_Pathloss=the average of the top 10%
FB to FB UE path losses; Pathloss_adjustment=the absolute value of
[1/2.times.(Avg_FBL_Pathloss-Maximum allowed FB Pathloss)]
[0094] Maximum allowed femtocell basestation pathloss is supplied
by the management system, and based on an assumed maximum indoor
path loss (typically around 90 dB).
[0095] Indoor loss is set at the value of minimum indoor loss, as
described with reference to FIG. 7.
[0096] In step 270, Avg_Ec/Io is compared with the desired
femtocell basestation UE CPICH Ec/Io. If Avg_Ec/Io is larger, then
the process moves to step 274, which compares Avg_FBL_Pathloss with
the maximum allowed femtocell basestation path loss. If
Avg_FBL_Pathloss is smaller, the UL and DL maximum transmit powers
are kept at the same level (step 275).
[0097] If Avg_FBL_Pathloss is greater than the maximum allowed
femtocell basestation path loss, then the UL and DL maximum
transmit powers are set as follows (step 276). Maximum DL power is
set at UE.sub.Prx, min, plus the indoor loss, minus
Pathloss_adjustment. Maximum UL power is set at FB.sub.Prx, min,
plus the indoor loss, minus Pathloss_adjustment. Minimum indoor
loss is reset at indoor loss minus Path loss_Adjustment
[0098] If it is determined, in step 270, that Avg_Ec/Io is smaller
than the desired femtocell basestation UE CPICH Ec/Io, the process
moves to step 272, where Avg_FBL_Pathloss is again compared with
the maximum allowed femtocell basestation path loss.
[0099] If Avg_FBL_Pathloss is smaller, the maximum DL power is set
in step 277 at UE.sub.Prx, min, plus the indoor loss, plus
Pathloss_adjustment. Maximum UL power is set at FB.sub.Prx, min,
plus the indoor loss, plus Pathloss_adjustment. Minimum indoor loss
is set at Indoor loss plus Pathloss_Adjustment.
[0100] If Avg_ML_Pathloss is greater than Avg_FBL_Pathloss, then an
error alert is sent to the management system (step 278).
[0101] Once the maximum DL and UL powers have been set in step 276
or 277, the process moves in parallel to steps 278 and 279. In step
279 the process checks whether the maximum DL power is greater than
or less than the maximum permitted femtocell basestation DL power
(a parameter set by the management system). If it is less than the
maximum permitted power, the maximum DL power remains at its re-set
value. However, if the maximum DL power is greater than the maximum
permitted power, the maximum DL power is changed to the maximum
permitted power, and a warning sent to the management system. For
example, a flag may be set to indicate that the maximum DL power is
less than that required to run a particular speech or data
service.
[0102] In step 279 the process checks whether the maximum UL power
is greater than or less than the maximum permitted femtocell
basestation UL power (a parameter set by the management system). If
it is less than the maximum permitted power, the maximum UL power
remains at its re-set value. However, if the maximum UL power is
greater than the maximum permitted power, the maximum UL power is
changed to the maximum permitted power, and a warning sent to the
management system. For example, a flag may be set to indicate that
the maximum UL power is less than that required to run a particular
speech or data service.
[0103] The whole process as described by FIGS. 6 and 8 repeats,
adapting the maximum UL and DL powers until either an error event
occurs, the powers converge to an optimal value or the host
processor identifies that there has been a significant change in
the local interference levels and the carrier, scrambling code and
initial UL and DL powers need to be re-evaluated. Again, the value
of minimum indoor loss is also adapted as the process repeats.
[0104] The maximum DL transmit power will also be adapted based on
reported round trip time (RTT) measurements available from the
femtocell basestation and measured for each femtocell basestation
UE. A histogram of the RTT measurements would be built up for all
calls and the maximum DL transmit power adapted so that a
predetermined number of RTT samples (typically 90%) are within the
expected coverage area.
[0105] Furthermore, Random Access Channel (RACH) measurements can
be used to determine at what distance from the access point a
mobile is trying to set up a call. If the call set up is outside of
the expected coverage area then the call can be rejected.
[0106] Error conditions such as multiple accesses from unregistered
mobiles may indicate that the DL coverage is too large or that the
user has positioned the femtocell basestation in a position that is
causing unnecessary DL macrolayer interference (e.g. on a window
overlooking the city). In this situation the maximum DL transmit
power may be reduced until this error event falls below a
predetermined threshold. Alternatively, the problem could be
reported to the management system, which may send a message to the
user requesting him to relocate the unit in a position that would
cause less interference. Thus the basestation can use knowledge of
access attempts by unregistered mobiles to adapt the DL and UL
maximum transmit powers.
[0107] As described above, there are several ways in which error
conditions can be detected, and may be reported to the management
system. For example, there may be a requirement to use a particular
power level, or information about a number of access attempts from
mobiles that are outside the intended coverage area. These may
indicate that the configuration of the basestation would cause
excessive interference, or otherwise be detrimental. In each of
these situations, the problem may be resolved by repositioning of
the basestation, for example away from a window or towards a
position nearer the centre of the intended coverage area. In
response to an error condition, therefore, a message may be sent
from the management system to the user of the basestation,
requesting that the basestation be repositioned. The message may be
displayed on the basestation itself, or sent to a device that is
connected to the basestation. This repositioning can be carried out
until the error condition is resolved, and therefore acts as a
pseudo-closed loop control.
[0108] There are thus described methods of operation of a
basestation, and basestations adapted for such uses, that allow the
basestations to configure themselves for operation within the
cellular network without excessive interference with each other or
with other basestations in the network.
* * * * *